The present invention relates to a method for use in underground mining for detecting the presence of persons in mining faces supported by support frames in which detection sensors are provided on at least some of the support frames, and which are coupled to control units for the support frames, whereby the detection sensors sample at least the working and operating area of a support frame to which they are assigned and bring that frame to a standstill or do not permit its movement, if the presence of a person is established in a detection area. The present invention further relates to a device for use in underground mining for the detection of the presence of persons in mining faces supported by support frames, whereby detection sensors are provided on at least some of the support frames, and are coupled to control units for the support frames, and which sample at least the working and operating areas of the associated support frames.
In modern mining of coal or other minerals by underground mining, extraction is commonly effected using a coal-extraction machine operating back and forth between two headings, for instance a shearing machine or an extraction plough. The roof of the face is underpinned and supported by a multiplicity of support frames arranged alongside each other, which are normally all attached to a conveyor for the removal of the coal or materials extracted onto it, to which the extraction machine also leads. Following the passage of the extraction machine the conveyor and the support frames are moved forward in the direction of the mining face, to which end following the pushing forward of the conveyor, the individual support frames are retracted (withdrawn) a little, then, with the aid of an advancing cylinder, are drawn forward (advanced) in the direction of the conveyor, and then the roof caps of the support frames are extended, until the prescribed support pressure is reached and the roof is again safely underpinned (setting). This method of operation of such an advancing support frame is well known.
In modern mining, each support frame is commonly provided with its own electrical or electro-hydraulic control unit, can be connected together for the exchange of information with each other, by means of which also dependent movement sequences can be performed by several support frames arranged alongside each other. The various movements of a support frame can be initiated automatically from a supervising control monitor and independently performed; it is also possible, however, to move a selected support frame manually via the keyboard of a control unit, whereby in this case the manual operation is not carried out from the control unit arranged on the support frame to be moved, but from the control unit on an adjacent support frame, which is connected by a control line to the control unit of the support frame to be moved (Isleworth safe distance support advance control).
A movement of a support frame, i.e. the retraction of the roof cap (withdrawal), advancing in the direction towards the face conveyor and re-extension of the roof cap (setting), should only occur when there is no person in the working and operating area of the individual support frame, so as to avoid accidents involving personal injury. The working and operational area of a support frame is to be understood to be that area bounded by the roof cap, the ground shoes, the rear gob shield and the face conveyor arranged in front of it, that is, that section of a face which is supported by the support frame. In order to avoid a movement of the support frame, whilst persons are to be found in this area, monitoring devices and procedures are installed, which only permit withdrawal, advancing and setting of the frame if no persons are put in danger thereby.
A method and a device of the construction described in the opening paragraph of the present specification are proposed in DE-OS 36 27 174, in which detection sensors are arranged on the support frames such that each sensor transmits a continuous signal in order to monitor an individual detection area. The method requires that each individual person at the face carries a transponder, which is a small transmitting and receiving device, which works with the detection sensors on the individual support frames, and is located by a sensor if the person is within the detection area of that individual sensor. As soon as a sensor receives a signal from the transponder, it passes a control signal to the control unit of the support frame, following which the control unit puts the normal control function of the support frame out of action and prevents movement of the support frame as long as the person is within the working and operational area of the support frame.
This device and this method have the disadvantage that all the detection sensors at the face are permanently active, which results in a relatively heavy current usage, which must be covered by expensive and intrinsically safe power circuits. Owing to the permanent activation of all the sensors at the face, the transponders carried by the individual persons are also permanently active and have a large energy requirement, which must be covered by transportable energy supplies such as batteries or accumulators and which, with a minimum operating duration of ten hours are relatively large and heavy. Furthermore, the detection sensors transmit permanent electromagnetic signals, which lead to a non-negligible electro-smog at the face, which can affect the health of the persons working at the face, and possibly influences their concentration, which can endanger the safety of the miners. Furthermore, false switching can easily occur owing to the permanent activation of all the -sensors and the electromagnetic waves transmitted by them, if the electromagnetic signal transmitted by one sensor is distorted, possibly after multiple reflections or similar, and is misinterpreted as the signal of a transponder by another detection sensor, and can lead to the immobilisation of a support frame in whose working and operating area there is no miner and which therefore could be moved without danger.
It is an aim of the present invention to address one or more of these disadvantages, and to produce a method and a device of the construction described at the beginning of the present specification, in which electro-smog at the face owing to the detection sensors is avoided and by which the current requirement not only of the detection sensors, but also of the transponders carried by the supervising personnel is small.
Accordingly the present invention is a method according to the opening paragraph of the present specification in which the detection sensors can be activated by the control units of the support frame and are activated before a planned movement of the support frame and de-activated after the completion of the movement.
Advantageously each support frame is provided with at least one detection sensor. It is alternatively possible to provide detection sensors only on alternate support frames and having the detection area of the sensors is large enough such that the working and operating areas of two adjacent support frames can be monitored together.
Preferably the detection sensor of a support frame to be moved is activated at a time before the planned support frame movement, and then the working and operating area of at least the support frame concerned is sampled, and a stop signal is transmitted to the control unit if the presence of a person is established during the sampling, or a release signal is transmitted if no person is established in the detection area during the sampling. Thus detection sensors at the face are thus only activated by the control units of the support frame to which the sensors are allocated when a movement of the support frame is shortly to occur. Normally a movement of the support frame is announced by a warning signal some five seconds before the start of the movement sequence. At about the same time the detection sensors assigned to the support frame to be moved are activated, which, after their activation, sample the working and operating area of the support frame concerned to establish whether a person is in the area. The sensor remains activated until the movement sequence of the support frame (withdrawal, advancing, setting) is completely finished and is then switched off by the associated control unit. In accordance with the present invention, therefore, the sensors arranged on the support frame are de-activated most of the time and are only switched on when the support frame is to be moved. By this selective control of the individual sensors the current requirement is small and the strain on the miners due to electro-smog is negligibly small or largely absent.
Preferably the sampling of the working and operating area of the support frame is effected according to an active/passive strobing process, in which the persons at the face are equipped with a transponder device, which is activated by an activated detection sensor if a person enters the sampled detection area of the detection sensor or is present in the area, and which then transmits a signal of the person""s presence to the detection sensor, in consequence of which the detection sensor transmits a stop signal to the associated control unit. Since in this embodiment of the invention the transponder device, worn for instance by a miner on his helmet or belt, is only activated when the miner is in the working and operating area of a support frame which is shortly to be moved, and correspondingly only transmits a signal of his presence at all in this comparatively infrequent situation, the current requirement of the transponder device is small, since it is for most of the time in xe2x80x9cstand-byxe2x80x9d mode which has a low energy requirement. It is therefore sufficient for the current supply to the transponder to be provided by a comparatively small, and thereby light, battery or an accumulator.
In a preferred embodiment the detection sensors sample their individual detection areas cyclically with a cycle time between 2 and 200 milli-seconds. Advantageously the cycle time lies in the range of 10 to 100 milliseconds. This means that a person who comes within the detection area of a sensor and into the working and operating area of the corresponding support frame is detected within a very short cycle time, in any case less than 0.2 seconds, and the presence of the person is indicated by the output of the stop signal to the control unit so that even a support frame already in movement can be brought to a standstill in a fraction of a second, so as not to endanger the person in the danger area.
Preferably the signals generated by the detection sensors are direct current signals with variable voltage amplitude. Advantageously the signals generated by the detection sensors have binary values and the information to be transmitted is coded by serial protocols. Therefore, the direct current signals with variable amplitude can be detected and evaluated by the control unit and, using suitable logging devices a logging not only of the stop and release signals emitted from the detection sensors, but also of inputted operating conditions or similar is possible.
Preferably the detection area of each detection sensor includes the working and operating area of the associated support frame and at least a part of the working and operating areas of the adjacent support frames. A detection sensor can thereby not only establish whether a person is present within the working and operating area of the associated support frame which is to be moved or is already moving, but can also detect whether a person comes into the working and operating area of the support frames adjacent to the moving or soon-to-be-moved support frame and possibly will shortly reach the working and operating area of this frame, so that its movement can be prevented or stopped before the person enters the actual danger zone.
Advantageously, the detection sensors cyclically perform a self test. Preferably the self test of a detection sensor is only performed if following its activation and sampling of the detection area, no person is detected. By the self test of the sensors fault conditions are very quickly recognised and can be reported to the control unit of the support frame.
Another aspect of the present invention is directed to a device as described in the opening paragraph of the present specification in which the detection sensors can be activated and de-activated by the control units of the associated support frames.
Advantageously, the detection sensors can be adjusted for different sizes of working and operating areas of the support frames. This means that fault messages from a sensor can be avoided, which otherwise could arise from non-alignment of the sensor to the height, width and depth of the support frame in its operating condition.
Preferably the detection sensors monitor the detection area cyclically with a cycle time of not more than 0.2 s.
Advantageously the detection sensors are housed in protective housings, where they are protected from the rough conditions in underground mining.
Preferably the device is further provided with listing arrangements for capturing and listing the adjustment of the detection sensors.
Advantageously the detection sensors are connected via control signal lines to the control units.
Preferably, the detection sensors operate in the intrinsically safe power range. This is well known in underground mining and is frequently required and reduces danger from fire-damp.
Preferably, the detection sensors are mounted on the roof caps of the support frames. Alternatively, they are positioned on the props of the support frames.
In a preferred embodiment indicating devices are provided for the detection sensors.
Preferably the indicating devices comprise light emitting diodes or similar.
Advantageously, the detection sensors each comprise a transmitter unit and a receiver unit, in which the transmitter unit transmits a signal for the activation of a transponder device carried by a person within the detection area, and the receiver unit receives a signal transmitted from the activated transponder device. The latter signal is sent on to a monitoring unit, which evaluates it and passes it as a control signal for the interruption of the support frame movement to the control unit of the support frame concerned.
Preferably the transmitter unit has a magnetic field antenna arrangement with two ferrite coil antennae arranged substantially in parallel and connected in equal phase. Advantageously the two ferrite coil antennae are each connected in series with a capacitor. Preferably, the ferrite coil antenna are arranged alongside each other on and substantially parallel to the roof cap of the individual support frame. This configuration generates a common, mutually assisting and magnetically amplified field with a substantially elliptical propagation in the plane. The greater half-axis of the ellipse runs between the two antennae, parallel to them, and the smaller half-axis runs at right angles to the direction of the antenna length. The shape of the field can thereby be matched to the ground plan shape of the individual support frame, so that it is possible, using one transmitter unit in each case, to monitor the support frame completely, which is longer than it is broad, without however detecting the immediately adjacent support frame. Advantageously, the longitudinal direction of the ferrite coil antennae runs substantially at right angles to the longitudinal direction of the face. For optimum matching of the two antennae to the dimensions of the individual support frame, it is expedient if the antennae are attached to the support frame with an adjustable separation between them.
Preferably the receiver unit has three receiver coils arranged at angles to each other. It is thereby possible to receive a solely one-dimensional signal of a person""s presence generated by a transponder device reliably and independently of the direction in which the signal of the person""s presence is in fact radiated from the transponder device. Advantageously, the three receiver coils of the receiver unit are arranged at right angles to each other.
In a preferred embodiment, the transponder device has a receiver device and a transmitter element, which on receipt, by the, receiver device, of the signal transmitted by the transmitter unit, is activated by it. Advantageously, the receiver device has three individual receivers arranged at angles to each other. Preferably, the individual receivers are arranged at right angles to each other.
Advantageously, the ferrite coil antenna of the transmitter unit are operated at a frequency between 7 and 11 kHz. Preferably the frequency is 9 kHz.
Advantageously, the ferrite coil antennae are arranged on the support frame at a distance from each other of between 100 and 180 mm. Preferably the distance is between 120 and 150 mm. This gives the desired elliptical field shape for outer dimensions of a support frame of some 4 times 1.5-2 m.
In a preferred embodiment, the signal of a person""s presence generated by the activated transmitter element of the transponder device is transmitted at a frequency between 1.5 and 2.5 MHz. In trials a frequency of 2 MHz has proved especially practicable, which is certainly high enough to exclude interference with other electronic components below the surface, and on the other hand is still low enough to generate the desired magnetic field.